Laminate flooring usually comprise of a core of 6-11 mm fibreboard, a 0.1-0.8 mm thick upper decorative surface layer of laminate and a 0.1-0.6 mm thick lower balancing layer of laminate, plastic, paper or like material. The surface layer provides appearance and durability to the floorboards. The core provides stability, and the balancing layer keeps the board plane after pressing and when the relative humidity (RH) varies during the year. The floorboards are laid floating, i.e. without gluing, on an existing subfloor. Traditional hard floorboards of this type were usually joined by means of glued tongue-and-groove joints. However the majority of all laminate floorboards are presently joined mechanically by means of so-called mechanical locking systems. These systems comprise locking means, which lock the boards horizontally and vertically. The mechanical locking systems are usually formed by machining of the core. Alternatively, parts of the locking system may be formed of separate materials, for example aluminium or plastic, which are factory integrated with the floorboard.
The main advantages of floating floors with mechanical locking systems are that they can easily and quickly be laid by various combinations of angling and snapping. They may also easily be taken up again and used once more at a different location.
The most common core material is a fibreboard with high density and good stability usually called HDF—High Density Fibreboard. Sometimes also MDF—Medium Density Fibreboard—is used as core.
A laminate board which comprises a surface of melamine impregnated decorative paper, plastic, wood, veneer, cork and the like are made by the surface layer and preferably a balancing layer being applied to a core material that in addition to HDF may be made of plywood, chipboard, plastic, and various composite materials. Recently a new board has been developed where a powder, comprising fibres, binders, wear resistant particles and colour pigment, is scattered on a core material and cured by heat and pressure to a solid paper free surface.
As a rule, the above methods result in a laminate board, which is divided by sawing into several panels, which are then machined to provide them with a mechanical locking system at the edges. A laminate board of the size of a panel, which is not necessary to divide, may be produced by the above method. Manufacture of individual floor panels usually takes place when the panels have a surface layer of wood or veneer.
Floorboard with mechanical locking systems may also be produced from solid materials such as solid wood.
In all cases, the above-mentioned floor panels are individually machined along their edges to floorboards. The machining of the edges is carried out in advanced milling machines where the floor panel is exactly positioned between one or more chains and belts, so that the floor panel may be moved at high speed and with great accuracy past a number of milling motors, which are provided with rotating diamond cutting tools or metal cutting tools and which machine the edge of the floor panel. By using several milling motors operating at different angles, advanced joint geometries may be formed at speeds exceeding 200 m/min and with an accuracy of about ±0.05 mm. The accuracy in the vertical direction is generally better than in the horizontal direction since it is difficult to avoid so called swimming which occurs when panels move horizontally in relation to the chain/belt during milling.
Definition of Some Terms
In the following text, the visible surface of the installed panel, such as a floorboard, is called “front side”, while the opposite side of the floorboard, facing the subfloor, is called “rear side”.
By “horizontal plane” is meant a plane, which extends parallel to the front side. Immediately juxtaposed upper parts of two neighboring joint edges of two joined panels together define a “vertical plane” perpendicular to the horizontal plane.
The outer parts of the floorboard at the edge of the floorboard between the front side and the rear side are called “joint edge”. As a rule, the joint edge has several “joint surfaces” which may be vertical, horizontal, angled, rounded, beveled, etc.
By “locking system” are meant coacting connecting means, which connect the panels vertically and/or horizontally. By “mechanical locking system” is meant that joining may take place without glue.
By “angling” is meant a connection that occurs by a turning motion, during which an angular change occurs between two parts that are being connected, or disconnected. When angling relates to connection of two floorboards, the angular motion generally takes place with the upper parts of the joint edges at least partly being in contact with each other, during at least part of the motion.
By “up or upward” means toward the front side and by “down or downward” means toward the rear side. By “inwardly” is meant towards the centre of the panel and by “outwardly” means in the opposite direction.
By “carving” is meant a method to form a groove or a protrusion on an edge of a panel by carving a part of the edge to its final shape by one or several carving tool configurations comprising several non-rotating and fixed chip-removing surfaces located along the feeding direction.
Known Technique and Problems Thereof
With a view to facilitating the understanding of embodiments of the present invention, known mechanical locking system will now be described with reference to FIGS. 1a-1e. In applicable parts, the subsequent description of known technique also applies to the embodiments of the present invention described below.
As shown in FIG. 1a the floorboards have a tongue 10 and a groove 9 that locks the edges in a vertical direction. A strip 6, which extends along a first edge 1, protrudes from the edge and has a locking element 8 that cooperates with a locking groove 14 in the adjacent second edge 1′ and locks the edges horizontally.
It is evident from this figure and FIG. 1b, that since the mechanical locking systems have parts, such as the tongue 10 and the strip 6, that project beyond the upper joint edges, expensive waste W is created when the large board 1b is cut by a sawblade 20 into several floor panels and when the locking system is formed.
Even when individual floor panels are produced, for example floors of solid wood, as shown in FIG. 1c, considerable waste (W) is caused by forming the strip 6 and the tongue 10.
These systems and the manufacturing methods suffer from a number of drawbacks, which are above all related to cost and function.
The waste is mainly related to the long edge locking system, which generally is installed by angling. The total waste may be about 10 mm or more or about 5% in floorboards that have a width of about 200 mm. The waste in narrow floorboards with a width of for example 100 mm may be about 10%.
To counteract these problems, different methods are used. The most important method is to limit the extent of the projecting parts. This usually results in lower locking strength and difficulties in laying or detaching the floorboards.
Another method is to use separate materials, for example aluminium or plastic, to form the strip or the tongue. Such materials are generally not cost efficient in low cost floors with a surface layer and a core made of very cost efficient materials such as impregnated paper and HDF respectively.
It is known that a locking system may be formed with overlapping edges A, B and a lower tongue C as shown in FIG. 1d (WO 2005/068747 Valinge Innovation AB). Such locking system will not reduce the waste. The overlapping edge or small tongue A is mainly used to facilitate horizontal displacement between the edges. FIG. 1e shows a known locking system (WO 2006/043893 Valinge Innovation AB) that has a separate flexible tongue 10 attached above the strip 6 and that is mainly intended to lock the short edges with vertical folding or vertical snapping.